Identification of a Plasmid-Borne Chloramphenicol-Florfenicol Resistance Gene in Staphylococcus sciuri

Abstract

The 16.5-kbp plasmid pSCFS1 from Staphylococcus sciuri mediated combined resistance to chloramphenicol and florfenicol. The gene responsible for this resistance property, cfr, was cloned and sequenced. The amino acid sequence of the Cfr protein revealed no homology to known acetyltransferases or efflux proteins involved in chloramphenicol and/or florfenicol resistance or to other proteins whose functions are known.Staphylococcus sciuri is a common inhabitant of the physiological skin flora of most rodents, ungulates, carnivora, and marsupials. Although classified as rarely pathogenic (6), S. sciuri isolates have been obtained occasionally from cases of mastitis in goats (10) and bronchopneumonia in cattle (13). Antimicrobial resistance is common among S. sciuri isolates, and a number of plasmids carrying one or more resistance genes have been identified (11,13,14). Resistance to chloramphenicol (CM) in staphylococci has usually been associated with plasmid-borne cat genes (11, 13), whose gene products inactivate CM by diacetylation. CM acetyltransferases, however, are unable to inactivate florfenicol (FF), a fluorinated CM derivative which was licensed in Germany in 1995 as a therapeutic agent to control bacterial respiratory infections in cattle. Genes whose gene products mediate combined resistance to CM and FF by efflux of both drugs have been identified in gram-negative bacteria, such as Salmonella enterica serovar Typhimurium (2) and Photobacterium damselae subsp. piscicida, formerly known as Pasteurella piscicidae (5). In staphylococci and related organisms, FF resistance genes have not been described yet.An S. sciuri isolate obtained from the nasal swab of a calf suffering from an infection of the respiratory tract proved to be resistant to tetracycline, erythromycin, kanamycin, CM, and FF. Plasmid analysis revealed the presence of six plasmids in the size range between 1.5 and 16.5 kbp. Experiments involving transformation into protoplasts of Staphylococcus aureus RN4220 (12) and subsequent selection of the transformants on regeneration media containing 20 g of FF/ml (Essex, Munich, Germany) identified only the 16.5-kbp plasmid, designated pSCFS1, as the mediator of resistance to CM and FF. This plasmid also mediated resistance to erythromycin by an inducibly expressed ermC gene as confirmed by PCR analysis (7). Cloning experiments revealed that the ermC gene was located on a 2.5-kbp PstI fragment of pSCFS1 (data not shown). The original S. sciuri isolate and S. aureus RN4220:pSCFS1 showed FF MICs of 64 g/ml and CM MICs of 32 g/ml. Preincubation of these isolates in the presence of either 0.5 g of FF or 0.5 g of CM increased the FF MICs to 512 g/ml and the CM MICs to 64 g/ml, suggesting that pSCSF1-mediated resistance to FF and CM in both staphylococcal hosts is inducible by FF as well as CM. Plasmid pSCFS1 was mapped ( Fig. 1) and subjected to cloning experiments. Restriction fragments of pSCFS1 generated by the enzymes EcoRI and BclI-BamHI were cloned into pBluescript SKII ϩ . The recombinant plasmids ...

Use of antimicrobials in veterinary medicine and mechanisms of resistance

“…Moreover, the plasmid-borne gene, cfr, from Staphylococcus sciuri has been found to mediate combined resistance to chloramphenicol and florfenicol by a yet unidentified mechanism [62].…”

Antimicrobial resistance in staphylococci from animals with particular reference to bovine Staphylococcus aureus, porcine Staphylococcus hyicus, and canine Staphylococcus intermedius

“…Combined resistance to chloramphenicol and florfenicol mediated by efflux systems has been described in gramnegative bacteria. Recently a novel gene, cfr, which mediates resistance to chloramphenicol and florfenicol has been identified on a plasmid from a bovine S. sciuri isolate [92]. The cfr gene product neither exhibits topology of a membrane protein nor inactivates chloramphenicol and florfenicol.…”

Clinical and Microbiological Aspects of Linezolid Resistance Mediated by the cfr Gene Encoding a 23S rRNA Methyltransferase

“…In Europe, cfr was initially found on a plasmid of a bovine isolate of Staphylococcus sciuri (14,24), and its acquisition by animal isolates appears to have been influenced by the use of florfenicol in the veterinary industry (23) and the mobility of the DNA encoding it (12). Chloramphenicol is still used in Colombia, especially in the pediatric population, and although the use of phenicols in the veterinary industry is unknown in Colombia, it is likely that the acquisition of cfr might have been influenced by the use of the phenicol group of antibiotics in animals and humans.…”